LONDON (AP) ' Deep cracks are emerging in Britain's coalition government, with one of its top officials lashing out at Prime Minister David Cameron on Sunday for deciding to block European Union treaty changes designed to save the euro.

Deputy Prime Minister Nick Clegg called the decision "bad for Britain" and said he is "bitterly disappointed" over the outcome of last week's EU summit during which Britain was the only nation to reject a tighter fiscal alliance in the bloc aimed at ending Europe's worst financial crisis in generations.

"Now there is a danger that the U.K. will be isolated and marginalized within the European Union," Clegg said, warning that Britain is "retreating further to the margins of Europe."

He said he will now do everything he can "to ensure this setback does not become a permanent divide" in Britain's coalition government.

After the EU summit in Brussels, Clegg publicly backed Cameron's decision to reject the proposed new European treaty because it didn't contain adequate safeguards for Britain and wasn't in the country's interests.

But during an interview with BBC television on Sunday Clegg said that when Cameron told him of his decision during a 4 a.m. phone call on Friday, "I said this was bad for Britain. I made it clear that it was untenable for me to welcome it."

Clegg's criticism of Cameron's decision on national TV raised questions about the viability of the coalition government, but one analyst said it is not in danger of collapsing.

Steven Fielding, a professor of political history at the University of Nottingham, accused Clegg of "trying to have his cake and eat it, too" by going on TV to disagree with Cameron but insisting that the coalition will stand.

"Cameron's got them over a barrel," Fielding said of the Lib Dems because they joined the coalition as a junior party and need time in government to establish political credibility.

Last year, Clegg's party joined with Cameron's larger Conservative Party in Britain's first governing coalition since World War II following an inconclusive national election.

The coalition has an 84-seat majority in the 650-seat House of Commons. One of its biggest ideological differences involves EU rules and regulations and the degree to which they affect government decisions and London's standing as Europe's top financial market.

The Conservatives have long contained many so-called "euro-skeptics," while the Lib Dems are the most pro-EU of any major British party, including the opposition Labour Party.

Clegg has been repeatedly accused of betraying Lib Dem values by endorsing Cameron's austerity measures and decision to increase university tuition fees.

But Fielding said that "however embarrassed and humiliated" the Liberal Democrats may feel by the direction of the government, they left themselves "no alternative" but to go along with it by agreeing to form the coalition after finishing third in the last national election.

Some experts have questioned Cameron's decision to take such a hard line at the EU summit, saying he could leave the UK isolated by abandoning its long-standing strategy of acting both within and outside the bloc.

But William Hague, Britain's foreign secretary and a member of the Conservative Party, disputed Clegg's account, saying Sunday that the deputy prime minister had been on board with the government's negotiating position ahead of the EU summit.

"We are not marginalized, I can assure you of that," Hague told Sky News. "Our agreement is required in the EU to a whole range of other decisions that will be coming up over the next few months."

Cameron rejected the invitation to join 26 other EU members to approve changes to the bloc treaty in a move that isolated Cameron from the bloc and raised doubts about whether Britain realistically can remain an EU member.

Conservative lawmakers already have toasted Cameron's decision in Brussels, while other Liberal Democrats have criticized it.

On Sunday, Clegg suggested Cameron is hamstrung by the Conservative euro-skeptics, saying "of course things would have been different" if he had attended the EU summit, too. "I'm not under the same constraints from my parliamentary party that clearly David Cameron is," Clegg said.

But the deputy prime minister dismissed talk of a breakup of the coalition government.

"It would be even more damaging for us as a country if the coalition government was to fall apart," he said. "That would cause economic disaster for the country at a time of great economic uncertainty."

Still, Clegg did not shy away from rebuking the stance of his Conservative coalition partners, who have called for a public referendum on Britain's relationship with Europe and had urged Cameron to not give in at the summit.

"There's nothing bulldog about Britain hovering somewhere in the mid-Atlantic, not standing tall in Europe, not being taken seriously in Washington," Clegg said.

Conservative lawmaker Mark Pritchard struck back, accusing Clegg and his party of being "totally out of step" with public euro skepticism.

"Better to be a British bulldog than a Brussels poodle," Pritchard said.